Thermal degradation mechanism of wood treated by guanidine flame retardants

To study the correlation between thermal degradation behavior and flame retardation of wood and the mechanism of the thermal degradation, wood was treated with guanidine flame retardants. The samples were subjected to thermogravimetry (TG), differential thermal analysis (DTA) and IR spectra. Moreover, activation energies of thermal degradation were obtained following the Broido equation. The date show that, wood treated by guanidine dihydrogen phosphate and diguanidine hydrogen phosphate obtain good flame retardation, whose limiting oxygen indexes are in a range 39%-42% while their main decomposition occur at lower temperatures (< 300°C), and their activation energies of thermal degradation are decreased by about 60 kJ/mol, which is due to the reaction of dehydration, rearrangement and carbonization, resulting in formation of less flammable products and correspondingly more char. However, wood treated with guanidine carbonate and guanidine nitrate have poor flame retardation, though the main decomposition temperatures decreased, whose limiting oxygen indexes are below 26%, which is due to their main decompositions still including two stages at higher temperatures (> 300°C), resulting in large flammable volatiles.